1. Field of the Invention
The invention relates generally to a hard disk drive (HDD) system. More particularly, the invention relates to a head retraction circuit having a hold function that controls a head reading a disc so that the head is parked within a safety zone of the disc.
2. Description of Related Technology
FIG. 1 illustrates a plan view of a portion of the inside of a typical HDD system 15 that may, for example, be used as a non-volatile mass data storage device within a personal computer system (not shown). The HDD system 15 includes a disc 10, which has a safety zone 11 and a data zone 12, and a head 20 to read or write digital data on the disc 10. When the HDD system 15 is unpowered (i.e., the system 15 is not in operation), the head 20 is preferably parked within the safety zone 11 of the disc 10. As is known in the art, parking the head 20 within the safety zone 11 helps to prevent xe2x80x9ccrashesxe2x80x9d or contacts of the head 20 on the data zone 12 of the disc 10, thereby preventing the inadvertent loss of data due to mechanical damage of the data zone 12 of the disc 10.
In operation, the HDD system 15 uses a spindle motor (not shown) to rotate the disc 10 at a predetermined speed and a voice coil motor (VCM) that moves the head 20 radially over the data zone 12 of the rotating disc 10 to read and/or write digital data thereon. Control of the spindle motor and the VCM is typically accomplished using a microprocessor or microcontroller (not shown) that executes a control program and which provides the appropriate control signals to the motors.
Initially, the HDD system 15 is unpowered, the disc 10 is not rotating, and the head 20 is preferably parked within the safety zone 11 of the disc 10. When power is applied to the HDD system 15, the microprocessor provides signals to the spindle motor so that the disc 10 is caused to rotate at a predetermined velocity. When the disc 10 reaches the predetermined velocity, the microprocessor provides signals to control the VCM so that the head 20 exits the safety zone 11 and moves radially over the data zone 12 to read and write digital data thereon. Conversely, when power is removed from the HDD system 15, the microprocessor provides signals to the spindle motor to stop the motor and provides signals to the VCM so that the head 20 is retracted or parked within the safety zone 11.
FIG. 2 illustrates a block diagram of a conventional a head retraction circuit 5 for the HDD system 15 that provides an automatic retraction or parking function for the head 20. The head retraction circuit 5 includes a switching unit 1, a reference voltage generator 2, and first and second driver circuits 3, 4. The reference voltage generator 2 provides a substantially constant reference voltage to the switching unit 1. The switching unit 1, receives the reference voltage and control signals from the microprocessor (not shown) and provides control signals to the drivers 3, 4. The drivers 3, 4 convert the control signals to provide current signals to the VCM winding that retract the head 20 to the safety zone 11 of the disc 10.
FIG. 3 illustrates an exemplary detailed schematic diagram of the retraction circuit 5 shown in FIG. 2. As shown, the reference voltage generator 2 includes a resistor R2 and transistors Q17-Q20 having their base-collector terminals connected to provide a diode function. The resistor R2 and the transistors Q17-Q20 are connected in series across a supply voltage VCC to provide a substantially constant reference voltage of about 2.8 volts (i.e., four diode drops) to the switching unit 1.
The switching unit 1, includes transistors Q1-Q3 connected as shown. The base terminal of transistor Q3 receives the reference voltage from the reference voltage generator 2 and transistor Q1 receives an input signal (SWITCH) from the microprocessor. If the SWITCH input is high (i.e., the voltage on the base terminal of transistor Q1 is sufficient to forward bias the base-emitter of Q1) then transistor Q1 is ON and shunts across the collector-emitter of transistor Q2 so that transistor Q2 is OFF. As will be described in greater detail below, when transistor Q2 is OFF, both drivers 3, 4 are OFF so that no current is supplied to the VCM winding and the head 20 does not retract. Conversely, if the SWITCH input is low (i.e., about zero volts) then transistor Q1 is OFF and transistor Q3 uses the reference voltage at its base terminal to provide control signals via its emitter terminal to turn ON the drivers 3, 4 to supply current to the VCM winding and retract the head 20.
The first driver 3 includes transistors Q4-Q10 and resistors R3 and R4, all connected as shown. Those skilled in the art will recognize that transistors Q5 and Q6 are connected in a current mirror configuration so that the amount of current flowing through diode-connected transistor Q5 is caused to flow through the collector terminal of transistor Q6. When transistor Q6 conducts, a bias voltage is developed across resistor R3 and transistors Q7 and Q8. This bias voltage is coupled to the base terminal of transistor Q9 to turn ON transistor Q9. Transistors Q9 and Q10 are connected in a Darlington configuration having a common emitter output (OUT1), which is connected to the VCM winding. Thus, when Q9 is ON, Q10 is also ON and may conduct a large amount of current while a very small current (i.e., Q10 collector current divided by the product of the betas for Q9 and Q10) is provided to the base terminal of transistor Q9.
The second driver 4 includes transistors Q11-Q16 and resistors R6-R8, all connected as shown. Transistors Q12 and Q13 are connected in a current mirror configuration. Transistor Q14 and resistor R6 generate a bias voltage across the base-emitter junction of transistor Q15 via the current provided by current mirror transistor Q13. Transistor Q15 is connected to Q14 and R6 to amplify the current mirror current and to provide the amplified current to resistor R7 and the base terminal of transistor Q16. The amplified current mirror current is available to drive transistor Q16 to control the conduction through its collector terminal, which is connected to the VCM winding.
The switching unit 1 controls the ON/OFF condition of the drivers 3, 4 in response to signals from the microprocessor. In particular, when the microprocessor applies a high level signal to the base terminal of transistor Ql then Q1 is ON and shunts across the collector-emitter of transistor Q2, and Q2 is OFF. When Q2 is OFF, the current mirror transistors Q5 and Q12 of the drivers 3, 4 are OFF and output drive transistors Q10, Q16 are OFF so that no current is provided to the VCM to retract the head 20. Alternatively, when the microprocessor applies a low level retraction signal to the base terminal of transistor Q1, then Q1 is OFF and Q2 is ON so that the current mirror transistors Q5 and Q12 are operational. With the current mirrors operational, the output drive transistors Q10, Q16 of the drivers 3, 4 are both ON so that current is provided to the VCM winding to retract the head 20.
The above-described conventional head retraction circuitry is directly responsive to a retraction signal from the microprocessor and does not compensate for VCM momentum. As a result, because the motion of the head 20 at the time the switching unit 1 receives the retraction signal from the microprocessor is not determinate, the parked location of the head 20 can vary significantly. For example, if the VCM is moving the head 20 away from the safety zone 11 at the time the retraction signal is received by the switching unit 1, the momentum of the VCM may prevent the head 20 from being retracted sufficiently to be parked within the safety zone 11. Conversely, if the VCM is moving the head 20 toward the safety zone 11 at the time the retraction signal is received, the momentum of the VCM may cause the head 20 to retract too far so that it is parked inside the inner radius of the safety zone 11.
In accordance with one aspect of the invention, a head retraction circuit for supplying current to a voice coil motor (VCM) to retract a head into a safety zone of a disc includes a switching unit adapted to receive a retraction signal and to produce a first control signal in response to the retraction signal, a first driver coupled to the VCM and the switching unit and adapted to provide current to the VCM in response to the first control signal, a holding unit coupled to the switching unit and adapted to receive the first control signal and to subsequently produce a second control signal after a predetermined time interval, and a second driver coupled to the VCM, the holding unit, and the switching unit and adapted to provide current to the VCM in response to the second control signal, whereby the first and second drivers provide current to the VCM to retract the head into the safety zone after momentum in the VCM has substantially dissipated.
The invention itself, together with further objects and attendant advantages, will best be understood by reference to the following detailed description, taken in conjunction with the accompanying drawings.